Light emitting device and method for manufacturing the same

ABSTRACT

A light emitter including a substrate, at least one semiconductor layer of a first conductivity type formed on the substrate, at least one semiconductor layer of a second conductivity type formed on a partial region of the semiconductor layer of the first conductivity type, a first bonding electrode connected to the semiconductor layer of the first conductivity type and a second bonding electrode connected to an almost entire surface of the semiconductor layer of the second conductivity type, wherein the substrate is transparent to light emitted from a proximity of a junction between the semiconductor layer of the first conductivity type and the semiconductor layer of the second conductivity type, the second bonding electrode is formed to have an almost rectangular shape and a substantially minimum area for bonding, and sides of the emitter are disposed in three directions of the circumstance of the second bonding electrode.

TECHNICAL FIELD

[0001] The present invention relates to a light emitter and a method formanufacturing the same.

BACKGROUND ART

[0002] In recent years, semiconductor light emitters such as LEDs whichemit light in a range from ultraviolet to visible light have beenrealized by using nitride semiconductor materials typified by GaN, AlN,InN or a mixed crystal thereof.

[0003] These LEDs mainly utilize a sapphire substrate which is aninsulator as a substrate. Therefore, different from ordinary lightemitters, the LED is required to have both p-type and n-type electrodeson its surface and various structures have been proposed for thispurpose.

[0004] A conventional light emitter using a nitride semiconductormaterial will be detailed with reference to FIGS. 7(a) and 7(b).

[0005] In a light emitter shown in FIGS. 7(a) and 7(b), an n-GaN layer2, an InGaN light emitting layer 3, a p-GaN layer 4 and a p-transparentelectrode 6 are sequentially formed on a sapphire substrate 1. Asregards the n-Gan layer 2, in a partial region thereof, a part of thesurface of thereof is removed together with the InGaN light emittinglayer 3 and the p-GaN layer 4 which are formed thereon. An n-bondingelectrode 5 is directly connected to the region. Further, a p-bondingelectrode 7 is connected on a partial region of the p-transparentelectrode 6. Moreover, balls 8 and bonding wires 9 are connected to then-bonding electrode 5 and the p-bonding electrode 7.

[0006] In such a structure that both the p- and n-electrodes are drawnfrom a surface of a device, electric current basically flows in paralleldirections with interfaces of semiconductor layers in the device.Therefore, electric current flowing from a p-type layer through thelight emitting layer to an n-type layer hardly flows evenly through eachpart of the light emitting layer. As a result, distribution of lightemission intensity in a light emitting portion tends to be wide-spread.

[0007] To cope with this problem, the p-electrode may be formed on analmost entire surface of the light emitting layer 3. In order to letemitted light out of the light emitting layer 3, the p-electrode must bea transparent electrode. Accordingly, there is no choice but to use anextremely thin film, for example, a metal film of about 10 nm inthickness. However, it is difficult to bond wires on such an extremelythin film. Therefore, in the above-described light emitter, thep-transparent electrode 6 is formed as the p-electrode and the p-bondingelectrode 7 which has enough thickness and is opaque is formed on a partthereof.

[0008] However, in the above-described light emitter, even though thelayered structure thereof is contrived so that the emitted light can betaken out from an upper surface of the light emitter, it is stilldifficult to let out the light emitted just under the opaque p-bondingelectrode 7. That is, even if the p-transparent electrode 6 is providedon the entire surface of the light emitting layer 3, the light emittedjust under the p-bonding electrode 7 cannot be taken out because it isblocked by the p-bonding electrode 7. Therefore, it is a problem that animprovement in letting out the emitted light is not brought about.

DISCLOSURE OF THE INVENTION

[0009] According to the present invention, provided is a light emittercomprising:

[0010] a substrate,

[0011] at least one semiconductor layer of a first conductivity typeformed on the substrate,

[0012] at least one semiconductor layer of a second conductivity typeformed on a partial region of the semiconductor layer of the firstconductivity type,

[0013] a first bonding electrode connected to the semiconductor layer ofthe first conductivity type, and

[0014] a second bonding electrode connected to an almost entire surfaceof the semiconductor layer of the second conductivity type,

[0015] the light emitter being characterized in that the substrate istransparent to light emitted from a proximity of a junction between thesemiconductor layer of the first conductivity type and the semiconductorlayer of the second conductivity type,

[0016] the second bonding electrode is formed to have an almostrectangular shape and a substantially minimum area for bonding, and

[0017] sides of the emitter are disposed in three directions of thecircumference of the second bonding electrode.

[0018] Further, according to the present invention, provided is a lightemitter provided with;

[0019] a substrate,

[0020] at least one semiconductor layer of a first conductivity typeformed on the substrate,

[0021] at least one semiconductor layer of a second conductivity typeformed on a partial region of the semiconductor layer of the firstconductivity type,

[0022] a first bonding electrode connected to the semiconductor layer ofthe first conductivity type, and

[0023] a second electrode connected to an almost entire surface of thesemiconductor layer of the second conductivity type,

[0024] the light emitter being characterized in that the substrate istransparent to a light emitted from a proximity of a junction betweenthe semiconductor layer of the first conductivity type and thesemiconductor layer of the second conductivity type,

[0025] the second electrode includes a second bonding electrode and asecond transparent electrode,

[0026] the second bonding electrode is formed to have an almostrectangular shape and a substantially minimum area for bonding, and

[0027] sides of the emitter are disposed in three directions of thecircumference of the second bonding electrode.

[0028] Still further, according to the present invention, provided is aprocess for manufacturing a light emitter comprising:

[0029] forming at least one semiconductor layer of a first conductivitytype, at least one semiconductor layer of a second conductivity type, afirst bonding electrode and a second bonding electrode, in pluralnumbers in a longitudinal and a transverse direction on a substrate, thesemiconductor layers of the first conductivity type and of the secondconductivity type and the first and second bonding electrodes being toconstitute a plurality of light emitters; and

[0030] separating the resulting substrate into units of light emitters,

[0031] wherein the semiconductor layers and the electrodes are disposedin such a manner that, in the longitudinal direction, the first bondingelectrodes are in juxtaposition with each other and the second bondingelectrodes are in juxtaposition with each other, and in the transversedirection, the first bonding electrodes are adjacent to the secondelectrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIGS. 1(a) and 1(b) illustrate a light emitter of the presentinvention,

[0033]FIG. 1(a) is a schematic plan view and

[0034]FIG. 1(b) is a schematic sectional view.

[0035]FIG. 2 is a schematic plan view illustrating a disposition oflight emitters of the present invention on a wafer in a process formanufacturing the same.

[0036]FIG. 3 is a diagram illustrating a disposition of electrodes oflight emitters to perform a comparative experiment on a radiativeefficiency.

[0037]FIG. 4 is a graph illustrating a light emission intensity of eachlight to light emitted from the light emitter to be obtained, that is,its absorption of light having wavelengths near the wavelength of theemitted light needs to be small enough as compared with itstransmission. For example, it can be selected from semiconductorsubstrates such as of silicon, germanium and the like, compoundsemiconductor substrates such as of SiGe, SiC, GaP, GaAsP, GaN and thelike, and dielectric substrates such as of sapphire, quartz, ZnO and thelike depending on the wavelength of the emitted light.

[0038] The semiconductor layer of the light emitter according to thepresent invention is comprised of at least one semiconductor layer ofthe first conductivity type and the second conductivity type to form atleast one pn junction. The first conductivity type and the secondconductivity type referred herein signify any of p-type, n-type ori-type.

[0039] These semiconductor layers may be formed of semiconductors havingthe same composition or semiconductors having different compositions.There may also be intermediate layers or buffer layers of the firstconductivity type, of the second conductivity type or of a conductivitytype different from these two types between the substrate and thesesemiconductor layers, between the semiconductor layers, between thesemiconductor layers and the first bonding electrode or the secondelectrode.

[0040] Examples of the semiconductor include nitride semiconductors ofgroup III, that is, gallium nitride semiconductors such asIn_(s)Al_(t)Ga_(1-s-t)N (0≦s, 0≦t, s+t≦1), as well as Al_(s)Ga_(1-s)As(0≦s≦1), Ga_(s)As_(1-s)P (0≦s≦1), In_(s)Ga_(1-s)As_(x)P_(1-x)(0≦s≦10<x≦1), In_(s)Al_(t)Ga_(1-s-t)P (0≦s, 0≦t, s+t≦1),In_(s)Al_(t)Ga_(1-s-t)N_(x)As_(1-x) (0≦s, 0≦t, s+t≦1, 0≦x≦1),In_(s)Al_(t)Ga_(1-s-t)N_(x)P_(1-x) (0≦s, 0≦t, s+t≦1, 0≦x≦1) andMg_(s)Zn_(t)Cd_(1-s-t)S_(x)Se_(y)Te_(1-x-y) (0≦s, 0≦t, s+t≦1, 0≦x, 0≦y,x+y≦1). Among them, gallium nitride semiconductors, particularlyIn_(s)Al_(t)Ga_(1-s-t)N (0≦s, 0≦t, s+t≦1), are preferable.

[0041] These semiconductor layers may or may not contain impurities ofn-type or p-type, for example, C, Si, Ge, Sn, Be, Zn, Cd, Hg, Mg, O, S,Se, Te or the like in a concentration of about 1×10¹⁴ to 1×10²¹ cm⁻³.

[0042] The semiconductor layers can be formed by a known method such asan MOCVD (organic metal chemical vapor deposition) method, an MBE(molecular beam epitaxy) method, an MOMBE method, a GSMBE (gas sourcemolecular beam epitaxy) method or the like. Further, the impurities maybe doped simultaneously with the forming of the semiconductor layers ormay be doped by an ion implantation or a thermal diffusion method afterthe semiconductors are formed.

[0043] The semiconductor layer of the first conductivity type has anexposed region to which the first bonding electrode to be describedlater is connected, preferably with a surface layer of the region beingremoved. As to the size of the region to which the first bondingelectrode is connected, it may have an area required for bonding, forexample, about 50-300×50-300 μm² or about 5-50% of the whole area of thesemiconductor layer of the first conductivity type for composing onelight emitter. Further, the thickness of the removed surface layer maybe about 0.5-10 μm or about 10-70% of the whole thickness of thesemiconductor layer of the first conductivity type.

[0044] As a method for partially removing the surface of thesemiconductor layer of the first conductivity type, known methods can beused. Specifically, a wet etching method using a mask having an openingonly in a region to be partially removed and an acid solution or analkali solution, an RIE (reactive ion etching) method using variouskinds of gas or the like can be mentioned. For example, the RIE methodusing a gas containing a halogen element is effective for nitridesemiconductors of group III and in particular, Cl₂ gas and SiCl₄ gas canbe used.

[0045] The semiconductor layer of the second conductivity type is formedonly on a partial region of the semiconductor layer of the firstconductivity type. The size thereof can be suitably adjusted accordingto the light emission intensity and the like of the light emitter to befinally obtained. For example, about 30-90% of the whole area of thesemiconductor layer of the first conductivity type can be mentioned.

[0046] The semiconductor layer of the second conductivity type can beformed in the same manner as that of the first conductivity type. In thecase of processing it into a desired shape, it can be realized by thesame manner as the method for partially removing the semiconductor layerof the first conductivity type as described above.

[0047] Incidentally, each of these semiconductor layers is preferablyformed into a rectangular shape because the outward shape of an LED chipis usually rectangle. In the present application, the “rectangularshape” includes a square shape, a trapezoid shape, a parallelogram shapein addition to the rectangular shape and further includes these shapeswith a part or all of the edges thereof being rounded, i.e., a shapenear a semicircle, a shape near a semioval and the like so that thesesemiconductor layers can be disposed without wasting space in the LEDchip.

[0048] The first bonding electrode of the light emitter according to thepresent invention is an electrode formed on the semiconductor layer ofthe first conductivity type and can be formed with a common conductivematerial. Examples thereof include Al, In, Ga, Ni, Ti, Cu, Au, Ag, Cr,Si, W, WN, Pt, Pd, Ta, Sr and the like. These materials may be formedinto a single layer film or a layered film of Ti/Au, W/Au and the like.The thickness thereof is not particularly limited, but for example,about 0.5 μm or more, preferably about 1 μm or more to 10 μm or less arementioned. It may be of any size as long as it has an area required forbonding. For example, 50-300×50-300 μm² can be mentioned as describedabove. The shape thereof is not particularly limited, but a rectangularshape is preferable.

[0049] A method for forming the first bonding electrode can be suitablyselected taking materials to be used into consideration. For example,usable are a sputtering method, a vacuum deposition method, an EBdeposition method, an ion plating method, an MBE method, a platingmethod, a screen printing method and the like.

[0050] The first bonding electrode is usually provided with a wire forexternal electrical connection. Further, a ball may be provided so thatthe first bonding electrode is firmly connected with the wire. The wireand ball can be formed of generally used materials.

[0051] The second electrode of the light emitter according to thepresent invention is an electrode formed on an almost entire surface ofthe semiconductor layer of the second conductivity type.

[0052] For example, (1) in the case where the second electrode is formedonly for bonding with the semiconductor layer of the second conductivitytype, it can be formed in the same manner with the same materials intothe same thickness as described above. In this case, the secondelectrode is preferably formed to have a substantially minimum area forbonding, for example, about 50-300×50-300 μm², preferably about100-200×100-200 μm², or about 20-90% of the whole area of thesemiconductor layer of the first conductivity type for composing onelight emitter. This second electrode is preferably formed into arectangular shape or an almost rectangular shape. The thickness thereofmay be about 0.5-10 μm, for example. Further, the second electrode maypreferably be formed in such a manner that sides of the light emitterare disposed in three directions of the circumference of the secondelectrode, i.e., just under or almost just under three sides of thesecond electrode including an opposite side to a side nearest to thefirst bonding electrode and two sides adjacent to the opposite side.

[0053] Further, (2) in the case where the second electrode is formed forbonding with and applying current to the semiconductor layer of thesecond conductivity type, the second electrode is composed of a secondbonding electrode and a second transparent electrode. In this case, thesecond bonding electrode can be formed in the same manner with the samematerials into the same thickness as described above. The secondelectrode in this case is preferably formed into a substantially minimumarea for bonding as same as in the above (1), for example, about50-300×50-300 μm², about 5-60% of the whole area of the semiconductorlayer of the first conductivity type for composing one light emitter, orabout 10-90% of the whole area of the semiconductor layer of the secondconductivity type. The second bonding electrode may preferably be formedinto a rectangular shape or an almost rectangular shape. Further, thesecond bonding electrode may preferably formed in such a manner thatsides of the light emitter are disposed in three directions of thecircumference of the second bonding electrode, i.e., just under oralmost just under three sides of the second bonding electrode includingan opposite side to a side nearest to the first bonding electrode andtwo sides adjacent to the opposite side.

[0054] The second transparent electrode is electrically connected withthe second bonding electrode and may be formed from just under thesecond bonding electrode to cover an almost entire surface of thesemiconductor layer of the second conductivity type, or may be formed soas not to overlap the second bonding electrode except for securing theminimum contact with the second bonding electrode.

[0055] The second transparent electrode is formed of an electrodematerial allowing an efficient take-out of the light emitted from thelight emitter. Its light transmissivity to the emitted light ispreferably about 30-100%, for example. As the electrode material, forexample, metals such as Al, Au, Ni, Pd, Ti, Cr, Ta, Pt, Sr and the like,transparent conductive materials such as SnO2, ZnO, ITO and the like canbe used. These materials may be formed into either a single layer filmor a layered film. The thickness thereof can be suitably adjusted sothat a proper light transmissivity is provided when the above materialsare used, for example, preferably about 20 nm or less, more preferablyabout 15 nm or less. On the other hand, in order to uniform current in atransverse direction on the surface of the semiconductor layer,resistance in a transverse direction of the light transmitting electrodeitself needs to be small enough as compared with that of thesemiconductor layer. Therefore, the thickness thereof is preferablyabout 2 nm or more. Specifically, in the case where a layered film ofNi/Au, Pd/Pt or the like is used, the thickness in the range of about1-10 nm/1-10 nm is preferable. Further, where a single layer of Pt isused, the thickness is preferably in the range of about 2-20 nm, morepreferably, in the range of about 2-10 nm.

[0056] A method for forming the second transparent electrode can besuitably selected taking materials to be used into consideration.Examples thereof include a sputtering method, a vacuum depositionmethod, an EB method, an ion plating method, an MBE method and the like.

[0057] In this case, when it is viewed planarity, for example, the firstbonding electrode, the second transparent electrode and the secondbonding electrode which are formed in an almost square shape maypreferably be disposed in a row.

[0058] Further, according to the method for forming the above-describedlight emitter, each light emitter is not formed individually, but aplurality of the light emitter is formed in a lump, preferably. That is,at least one semiconductor layer of the first conductivity type, atleast one semiconductor layer of the second conductivity type, the firstbonding electrode and the second electrode are formed in plural numbersto constitute a plurality of light emitters, in the longitudinal andtransverse directions on the substrate. Then, the obtained substrate isdivided by the unit light emitter or, if required, by two or more unitlight emitters. In this case, the semiconductor layers and theelectrodes are preferably arranged in such a manner that the firstbonding electrodes are in juxtaposition with each other and the secondelectrodes are in juxtaposition with each other in the longitudinaldirection and the first bonding electrodes are adjacent to the secondbonding electrodes in the transverse direction. In the case where thesecond electrode is comprised of the second bonding electrode and thesecond transparent electrode, the first bonding electrodes arepreferably disposed adjacently to the second bonding electrodes in thetransverse direction.

[0059] Further, in the longitudinal direction, the first bondingelectrodes and the second electrodes may be formed separately injuxtaposition, but a plurality of first bonding electrodes or aplurality of second electrodes may be formed into one-piece.

[0060] The plural light emitters formed into one-piece as describedabove may be divided by a known method such as a scribing method, adicing method, a laser cutting method or the like.

[0061] According to the scribing method, the substrate is adjusted toabout 50-200 μm in thickness, and then the wafer is scribed with adiamond point and divided into chips along scribed grooves. According tothe dicing method, the substrate is adjusted to about 100-500 μm inthickness, then the wafer is cut by a rotary blade made of solidifieddiamond-ground particles and divided into chips. According to the lasercutting method, a CO₂ laser, an excimer laser or a YLF laser can be usedand a KrF excimer laser having a wavelength of 248 nm may be used forcutting a sapphire substrate.

[0062] Hereinafter, embodiments of the light emitter of the presentinvention and the method for manufacturing the same will be describedwith reference to the drawings, but the present invention is not limitedto these embodiments.

[0063] Embodiment 1

[0064] A blue light emitter of this embodiment is shown in FIGS. 1(a)and 1(b). In this light emitter 100, an n-GaN layer 102, an InGaN lightemitting layer 103 and a p-GaN layer 104 are sequentially formed on asapphire substrate 101 which hardly absorbs visible light and istransparent to the wavelength of light emitted by this light emitter. Ina partial region thereof, the surface of the n-GaN layer 102 ispartially removed together with the InGaN light emitting layer 103 andthe p-GaN layer 104 formed thereon and an n-bonding electrode 105 isdirectly connected to the region. A p-bonding electrode 107 is connectedto a partial region of a p-transparent electrode 106. Further, balls 108and bonding wires 109 are connected to the n-bonding electrode 105 andthe p-bonding electrode 107.

[0065] In this light emitter 100, the n-bonding electrode 105, thep-transparent electrode 106 and the p-bonding electrode 107 are disposedin a row. Incidentally, in FIG. 1(a), the balls 108 and the bondingwires 109 are omitted for easy understanding.

[0066] A method for forming the above-described light emitter is shownbelow.

[0067] First, the n-GaN layer 102, the InGaN light emitting layer 103and the p-GaN layer 104 are sequentially laminated on the sapphiresubstrate 101 of 300 μm in thickness.

[0068] Then, the p-GaN layer 104, the InGaN light emitting layer 103 anda partial surface of the n-GaN layer 102 are removed in the region wherethe n-bonding electrode 105 will be formed in a later step by aphotolithography technique and a dry etching technique.

[0069] Next, the p-transparent electrode 106 of a Ni/Au film having athickness of about 15 nm is formed on the p-GaN layer 104. In this case,the size of the p-transparent electrode 106 is about 150×350 m². Then,the n-bonding electrode 105 of an Al film having a thickness of about 1μm is formed on the n-GaN layer 102.

[0070] Further, the p-bonding electrode 107 of an Au film having athickness of about 1 μm is formed on the p-transparent electrode 106.This p-bonding electrode 107 is specially provided because wires are noteasily bonded to the p-transparent electrode 106 of an extremely thinmetal film. The size of the p-bonding electrode 107 is required to be assmall as possible taking the efficiency in letting out the emitted lightinto consideration, so that it is formed into a square shape with a sideof 200 μm.

[0071] Such steps are usually conducted in a lump to a plurality oflight emitters as shown in FIG. 2. That is, the bonding electrodes 105and 107 are formed jointly in plural numbers, and then divided intolight emitters 100 as units.

[0072] Before dividing into the light emitters 100, a characteristictest for the light emitters 100 is performed on the substrate 101. Thisis a step for testing whether desired characteristics are obtained withregard to an emitter voltage, light emission intensity and the like byapplying a probe to the p-bonding electrode 107 and the n-bondingelectrode 105 to apply electric current as appropriate. In thisembodiment, as shown in FIG. 2, a set of four light emitters 100 areformed to be joined to the bonding electrodes 105 and 107. Therefore,four light emitters can be tested in one time.

[0073] Moreover, according to the disposition as shown in FIG. 2, sincethe bonding electrodes 105 and 107 to which the probe is to be appliedare disposed successively in line, the test can be performed only bysliding probes along the bonding electrodes 105 and 107 without damagingthe p-transparent electrode 106 by mistake nor dropping dust and thelike on the p-transparent electrode 106 from the probes, for example.Accordingly, the yield of the process is improved.

[0074] Additionally, in the longitudinal direction of FIG. 2, sincestrictness is not required to mask positioning for constituting theelectrodes 105, 106 and 107 and the like of the light emitter, theproduction process is simplified.

[0075] In a later step, the light emitters shown in FIG. 2 are divided.The divided light emitters are lifted and transferred as required by acollet (a vacuum suction tool). In this case, if used is such a colletthat only contacts both ends of the light emitter (the sides where thep-bonding electrode 107 and the n-bonding electrode 106 are formedrespectively), both ends of the light emitter are fixed, which enables astable transfer of the light emitter. Moreover, since only the bondingelectrodes exist on both sides of the light emitter, a section forletting the emitted light out is not damaged. This is a specific effectof the light emitter of the present invention in which the n-bondingelectrode, the p-transparent electrode and the p-bonding electrode aredisposed in a row in this order so that only the bonding electrodes aredisposed on both sides of the light emitter.

[0076] Then, each light emitter is fixed on a suitable pedestal which isnot shown in FIG. 1 and bonding wires 109 are bonded onto the n-bondingelectrode 105 and the p-bonding electrode 107. At this time, balls 108are formed on the ends of the bonding wires 109, and thereby a firm wirebonding is completed.

[0077] In the above light emitter 100, as shown in FIG. 1(a), three ofthe four sides of the circumference of the square p-bonding electrode107 consist sides of the light emitter 100. That is, at the three sides,sides of the light emitting layer 103 and the substrate 101 which istransparent to the emitted light are exposed. Therefore, the lightemitted just under the p-bonding electrode 107 can be effectively takenout, which is not achieved sufficiently with the conventional lightemitter.

[0078] Effect on the light emission efficiency by the disposition of theelectrodes in the light emitter is experimented.

[0079] That is, as shown in FIG. 3, light emitters having their sidesalong three sides of the circumference of the p-bonding electrode 107 asin the above embodiment and light emitters having their sides along twosides of the circumference of the p-bonding electrode as shown in theconventional embodiment are formed with varying the area of the lightemitting portions. Current having the same current density is appliedand differences in the light emission intensity are compared.

[0080] The left column in FIG. 3 shows light emitters having their sidesalong three sides of the circumference of the p-bonding electrode.Supposing that the area of the p-bonding electrode is 1, shown are threetypes of light emitters whose light emitting portions have areas (thesum of the area of the p-bonding electrode and of the p-transparentelectrode) of 1, 2 and 3. For example, it is shown that an emitter whoselight emitting portion has an area of 1 is an emitter in which thetransparent electrode is not formed, and that an emitter whose lightemitting portion has an area of 2 is an emitter in which a transparentelectrode having the same area as the p-bonding electrode is formed.Further, the right column shows the light emitter having their sidesalong two sides of the circumference of the p-bonding electrode. Thearea of the light emitting portion is same as the above. In thisexperiment, the size of the p-bonding electrode is fixed to a squareshape having a side of 200 μm and a thickness of the sapphire substrateis fixed to 300 μm. An electric current of 10 mA per 1 area was applied.

[0081] The results are shown in FIG. 4. FIG. 4 relatively shows thelight emission intensity of each light emitter shown in FIG. 3.

[0082] According to the results shown in FIG. 4, the light emittershaving their sides along the three sides have greater light emissionintensity than the light emitters having their sides along the twosides, independently of the area of the light emitting portion.

[0083] From the results, it is found that taking out the light emittedjust under the p-bonding electrode is difficult even if thep-transparent electrode is provided adjacently to the p-bondingelectrode and that the best way to improve the taking-out of light is toprovide the sides of the circumference of the p-bonding electrode asemitter sides. Incidentally, such effect does not appear remarkably in alight emitter whose substrate is opaque to the emitted light. The reasonis that the emitted light is absorbed in the substrate and semiconductorlayers formed thereon when an opaque substrate is used, so that thelight emitted just under the p-bonding electrode is hardly taken out.However, when a transparent substrate is used, the light emitted justunder the p-bonding electrode can be taken out through sides of thesubstrate as far as the sides of the substrate are disposed at thecircumference of the p-bonding electrode.

[0084] In addition, the results in FIG. 4 are hardly changed where thethickness of the substrate is in the range of 60-400 μm or where thesize of the p-bonding electrode is in the suitable range of100-200×100-200 μm².

[0085] The smaller the size of the p-bonding electrode is, the moredesirable. However, it is necessary to ensure an area required forbonding. Further, the size of the light emitting portion needs to beproperly set to prevent the applied current density from beingexcessive. The reason is that if the applied current density isexcessive, the light emission efficiency may be deteriorated bygeneration of heat, or the life span of the emitter may be adverselyinfluenced. Therefore, in the p-electrode formed to cover the lightemitting portion, the minimum area required for bonding is for thep-bonding electrode and the rest of the area is used as thep-transparent electrode in order to secure a proper light emitting area.In addition, the p-transparent electrode is provided adjacently to onlyone side of the p-bonding electrode so as not to hinder the lightemitted just under the p-bonding electrode from being taken out.

[0086] Thus, according to the light emitter of Embodiment 1, the area ofthe p-bonding electrode is minimized and three sides of the p-bondingelectrode are disposed along the emitter sides, whereby the lightemitted just under the p-bonding electrode can be effectively taken outof the light emitter, resulting in an improvement of the light emissionefficiency of the light emitter compared with the conventional one.

[0087] Further, in this embodiment, since a nitride semiconductor ofgroup III element is used for each semiconductor layer, a light emitterhaving favorable characteristics which emits light in the visible rangecan be obtained.

[0088] Further, in FIG. 2, when the light emitters are divided by a unitof two, i.e., as represented by 110, a light emitter having twice aslarge an area for the light emitting portion as usual one can beobtained.

[0089] Thus, according to the method for manufacturing the light emitterof this embodiment, light emitters having different areas for the lightemitting portions can be obtained on one substrate only by partiallychanging the manufacturing process thereof.

[0090] Embodiment 2

[0091] A green light emitter of this embodiment is shown in FIGS. 5(a)and 5(b). This light emitter is substantially the same as that ofEmbodiment 1 except that the p-bonding electrode 107 is formed about30□m inside of sides of the emitter.

[0092] Further, in this embodiment, the sapphire substrate 101 is 100 μmthick, the p-transparent electrode 106 is a rectangular shape of 100×200μm and the p-bonding electrode 107 is in a square shape with a side of100 μm.

[0093] Even in the light emitter having such a structure, the lightemitted just under the p-bonding electrode 107 can be effectively takenout, as in Embodiment 1. That is, a light emitter which emits light inthe visible range and has a greater light emission efficiency comparedwith the conventional one is obtained.

[0094] Embodiment 3

[0095] A yellowish green light emitter of this embodiment is shown inFIGS. 6(a) and 6(b). This light emitter is substantially the same asthat of Embodiment 1 except that the p-transparent electrode is omitted.

[0096] Further, in this embodiment, the sapphire substrate 101 is 200 μmthick and the p-bonding electrode 107 is in a square shape with a sideof 150 μm.

[0097] In the light emitter having such a structure, since the area foremitting light becomes smaller, there is a problem of degradation incharacteristics such as deterioration of the light emission efficiencyunder high electric current. However, on the other hand, this lightemitter can be utilized in an LED device intended for a low outputoperation under low electric current. Therefore, a light emitter even insuch a simple configuration as shown in FIGS. 6(a) and 6(b) can besufficiently used.

[0098] Accordingly, even in this light emitter, the light emitted justunder the p-bonding electrode 107 can be effectively taken out from theemitter sides. Thus, the light emitter having sufficientcharacteristics, particularly aimed at a low output operation can beobtained.

[0099] According to the light emitter of the present invention, thelight emitted just under the second electrode, which is not effectivelyutilized conventionally, can be taken out from the emitter sides at themaximum level, thereby improving the efficiency in letting the emitterlight out.

[0100] Further, by disposing the semiconductor layers and the electrodesof the light emitter of the present invention in a suitableconfiguration, the light emitter can be formed in a convenient and easymanner.

What is claimed is:
 1. A light emitter comprising: a substrate, at leastone semiconductor layer of a first conductivity type formed on thesubstrate, at least one semiconductor layer of a second conductivitytype formed on a partial region of the semiconductor layer of the firstconductivity type, a first bonding electrode connected to thesemiconductor layer of the first conductivity type, and a second bondingelectrode connected to an almost entire surface of the semiconductorlayer of the second conductivity type, the light emitter beingcharacterized in that the substrate is transparent to light emitted froma proximity of a junction between the semiconductor layer of the firstconductivity type and the semiconductor layer of the second conductivitytype, the second bonding electrode is formed to have an almostrectangular shape and a substantially minimum area for bonding, andsides of the emitter are disposed in three directions of thecircumference of the second bonding electrode.
 2. A light emitterprovided with; a substrate, at least one semiconductor layer of a firstconductivity type formed on the substrate, at least one semiconductorlayer of a second conductivity type formed on a partial region of thesemiconductor layer of the first conductivity type, a first bondingelectrode connected to the semiconductor layer of the first conductivitytype, and a second electrode connected to an almost entire surface ofthe semiconductor layer of the second conductivity type, the lightemitter being characterized in that the substrate is transparent tolight emitted from a proximity of a junction between the semiconductorlayer of the first conductivity type and the semiconductor layer of thesecond conductivity type, the second electrode comprises a secondbonding electrode and a second transparent electrode, the second bondingelectrode is formed to have an almost rectangular shape and asubstantially minimum area for bonding, and sides of the emitter aredisposed in three directions of the circumference of the second bondingelectrode.
 3. The light emitter according to claim 2, wherein the firstbonding electrode, the second transparent electrode and the secondbonding electrode are disposed in a row.
 4. The light emitter accordingto any one of claims 1 to 3, wherein the semiconductor layer of thefirst conductivity type and the semiconductor layer of the secondconductivity type are formed of a nitride semiconductor of group IIIelements.
 5. A process for manufacturing a light emitter characterizedby comprising: forming at least one semiconductor layer of a firstconductivity type, at least one semiconductor layer of a secondconductivity type, a first bonding electrode and a second bondingelectrode which constitute a plurality of light emitters in pluralnumbers in a longitudinal and a transverse direction on a substrate, andseparating the resulting substrate into units of light emitters, whereinthe semiconductor layers and the electrodes are disposed in such amanner that, in the longitudinal direction, the first bonding electrodesare in juxtaposition with each other and the second bonding electrodesare in juxtaposition with each other, and in the transverse direction,the first bonding electrodes are adjacent to the second electrodes.